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Overview

The interface between the host computer and the Target system is electrically quite simple. It just use a serial port of the host computer to transfer byte oriented commands from the host to the HC(S)XX microcontroller after being translated by itself into the particular time multiplexed data frames which are understood by the HC(S)XX’s BDM system.

The logical translation mentioned above is performed by an inexpensive PIC16C745 microcontroller, running a firmware specially designed to be used with our ActiveX. This interface microcontroller enables the target system to operate at any frequency according to the operational specifications of the HCS08 family.

The schematic is shown below:

Board controls

-Reset button

The pod interface has a reset switch.. This button can be used to reset the pod microcontroller together with the Target processor. In normal operation, you should not need to reset the pod. The ActiveX should be able to handle target’s resets for you through an appropriate invocation of the the Reset method by your software.

-Led indicators

Two LED's are provided as feedback. The Red led indicates pod’s firmware writing operations to the target’s on-chip flash. The Green indicator lights up when RS232 commands are coming from the host. During downloads to memory, you may see a definite flashing of the green led. During a large memory dump, the green led may turn on and stay in that state for a while.

Pod connections

-RS232 Host connection

The interface use a female DB9 connector to establish an electrical connection with the host computer mean RS232. You must use a straight cable with at least pins 2, 3, 5, 7, and 8 connected. This is because the interface use a flow control by hardware so the pins 7 and 8 are very important. It is advisable to use a straight 9 conductor cable which you can get in most computer shops.

-Target Connection

Connection to the Target system is made through a modified version of the standard BDM cable. The standard BDM cable is made to connect to a six pin connector as shown below:

Our modified version use a 2x5 header instead of the 6 pins connector shown above. The target connection is shown below:

-Power supply

You have to provide 9 vdc to the board in order it can operate. The connector is a 1x3 pin header and it is shown below:

The PCB Layout

The dimensions of the board are approx. 3.24" by 1.48". Here you can see the components layout together with the top and the bottom side of the PCB.

Download Board & Schematic

The whole project (except the pod interface’s firmware) is freely available for use. The board and schematic files of the interface together with the ActiveX control and software samples which include source code can be downloaded from the project’s web site at no cost. The PIC16C745 burned with the firmware is available for only $47 US dollars. The .HEX of a RS232 version based on a PIC16F628 is available.  Contact me for more information.